Let me tell you a little story. I bought myself a new Ruger SR 556 a while back. I really like the gun. A tad heavier than some, but not a problem. Anyway, one day on the range I heard something odd. I didn't think much about it and kept shooting. Then it happened again. The Ruger starting mixing in a two or three round burst every mag. Please be aware that my Ruger is not selective fire. The bursts starting coming more often, and getting longer. Four to six round burst started happening. Not really wanting to send the rifle back for repair for who knows how long, I replaced the entire trigger group with a Rock River 2 stage trigger. The rifle calmed down some, now it would limit itself to a two round burst about every mag or so. Well, I sent the gun back to Ruger. They replaced the sear disconnector and test fired it 50 times. All is right. Wrong. I went to the range to rezero sights and optics. Thirity rounds of slow fire zero work. Change mags. On about round two or three, I wasn't really counting, the gun became a runaway and dumped the whole mag. Soooooooo, the gun has gone back to Ruger for another repair attempt. My guess is the bolt or upper receiver is out of spec and the bolt is riding too high to reset the hammer. I guess we shall see. Has anybody else ever had something like this happen?